塔里木盆地西北缘晚震旦世玄武岩地球化学特征及大地构造背景

Geochemical properties of late Sinian basalt in the northwestern boundary of Tarim basin and its tectonic setting

塔里木盆地是我国最大的沉积盆地，也是我国石油工业的重要战略接替地区．因此，探讨塔里木盆地的形成和演化具有十分重要的意义．在塔里木盆地西北缘的柯坪地区出露了一套晚震旦世玄武岩．晚震旦世的舒盖特布拉克组由碎屑岩夹有玄武岩组成．玄武岩主要由斜长石、辉石和少量橄榄石等组成，具有气孔－杏仁构造，间粒结构和辉绿结构．根据古植物化石和Ｕ－Ｐｂ同位素年代学的结果确定其年代为晚震旦世．通过对盆地西北缘晚震旦世玄武岩的岩石地球化学研究发现该玄武岩为一套来源于亏损地幔的板块内部碱性玄武岩．依据地球化学研究结果和沉积学特征，作者认为塔里木盆地西北缘在晚震旦世处于大陆边缘拉张的裂谷环境．这一研究成果对解决塔里木盆地早期的构造演化具有十分重要的意义．

Tarim basin is the biggest sedimentary basin in China,and it is also a important area of oil industry in the future.Therefore,it is very significant to study the evolution and formation of Tarim basin.A suit of late Sinian basalt exposed in Keping area in the northwestern boundary of Tarim basin.The late Sinian Sugaitebulak formation in Xiaoerbulake section in Keping is consist of detrital rocks intercalating with four basalt beds.Late Sinain basalt is composed of plagioclase,augite and olivine etc.with fumarole amygdaloidal structure,intergranular texture and diabasic texture.According to the results of palaeontological data of strata and the U Pb isotopic dating(740Ma),We can conclude that its formation times is late Sinian.Through the geochemical study on late Sinian basalt,authors find that the late Sinian basalt is intraplate alkaline basalt which originated form the partial melting of depleted mantle.Based on the geochemical results and sedimentary properties,we suggest that the tectonic setting of northwestern Tarim basin in late Sinian was rifted contiental margin.This discovery is very important for us to identify the tectonic evolution of Tarim basin.